Initiation circuit for a capacitor discharge ignition system

ABSTRACT

An initiation circuit for a capacitor discharge ignition system for an internal combustion engine having an ignition capacitor, a semiconductor trigger means for discharging the ignition capacitor in synchronism with the engine, an oscillator providing charging pulses for the ignition capacitor and an enabling circuit responsive to the operation of the semiconductor trigger to couple a signal to the oscillator to initiate the same with the enabling circuit including a transistor and zener diode coupled across the output of the transistor to a reference potential to prevent changes in supply potential from initiating the oscillator. A high voltage output transformer coupled to the semiconductor trigger provides a discharge path for the ignition capacitor.

United States Patent 1 4 Oct. 24, 1972 Vargas [54] INITIATION CIRCUITFOR CAPACITOR DISCHARGE IGNITION SYSTEM [72] Inventor: Robert .1.Vargas, Arlington Heights, Ill.

[73] Assignee: Motorola, Inc., Franklin Park, Ill.

[22] Filed: July 14, 1971 [21] Appl. No.2 162,580

[52] US. Cl ..123/148 E, 123/148 R [51] Int. Cl ..F02p 1/00 [58] Fieldof Search ..123/148 E [56] References Cited UNITED STATES PATENTS3,566,188 2/1971 Minks ..123/148 E 3,560,833 2/1971 Oishi ..123/148 E3,618,580 11/1971 Dogadko ..l23/148 E 3,433,208 3/1969 Dogadko ..123/148E 3,418,988 12/1968 Lewis ..123/148 E IGNITION SWITCH ALTERNATOR3,605,714 9/1971 Hardin 123/148 E Primary Examiner-Laurence M. GoodridgeAssistant Examiner-Ronald B. Cox

Att0rney-Mueller and Aichele ABSTRACT An initiation circuit for acapacitor discharge ignition system for an internal combustion enginehaving an ignition capacitor, a semiconductor trigger means fordischarging the ignition capacitor in synchronism with the engine, anoscillator providing charging pulses for the ignition capacitor and anenabling circuit responsive to the operation of the semiconductortrigger to couple a signal to the oscillator to initiate the same withthe enabling circuit including a transistor and zener diode coupledacross the output of the transistor to a reference potential to preventchanges in supply potential from initiating the oscillator. A highvoltage output transformer coupled to the semiconductor trigger providesa discharge path for the ignition capacitor.

5 Claims, 1 Drawing Figure DISTRIBUTOR DISTRIBUTOR PATENTED 0m 24 I972Inventor ROBERT J. VARGAS BY M [9m .mOkDmzmkwa ATTYS:

INITIATION CIRCUIT FOR A-CAPACITOR DISCHARGE IGNITION SYSTEM CROSSREFERENCE TO RELATED APPLICATION A related application (Ser. No.162,579) discloses the present invention.

BACKGROUNDOF THE INVENTION Permanent magnet altemators have beenproposed as power sources for enabling circuits of capacitor dischargeignition systems with resultant uneven ripples in the supply potentialbeing applied to the ignition circuit. Consequently in two and fourcylinder internal combustion engines which have been used in outboardboat motors, the saturable oscillator, or charging circuit, may beimproperly activated and the ignition capacitor charged above the limitfor which the discharge circuit was originally designed. Thisovercharging can lead to the eventual breakdown of the semiconductorcontrolled rectifier because of the application of high voltages. Theadded charging may also breakdown the dielectric material of theignition capacitor and shorten its useful life.

With high speed engines it is necessary to have the ignition capacitorfully charged prior to ignition. Some enabling circuits have been unableto respond quickly enough to initiate the oscillator charging circuit tofully charge the ignition capacitor prior to discharge.

An additional problem results from voltage turnoff spikes of thesaturable oscillator being applied to the anode of the semiconductorcontrolled electrode and shortening its useful life.

SUMMARY OF THE INVENTION It is an object of this invention to provide animproved initiation and capacitor discharge ignition system.

It is a further object of this invention to prevent overcharging of theignition capacitor of an initiation and capacitor discharge ignitionsystem.

It is yet another object of this invention to improve the response timeof the charging circuit in an initiation and capacitor dischargeignition system.

It is yet a further object of this invention to prolong the useful lifeof the semiconductor controlled rectifier trigger means in an initiationand capacitor discharge ignition system.

It is still another object of this invention to protect thesemiconductor controlled rectifier trigger means from high voltageturnoff spikes of the power transistor in an initiation and capacitordischarge ignition system.

With the closing of an ignition switch a supply potential is coupled tothe power transistor, and enabling transistor and a trigger transformerof the initiation and capacitor discharge ignition system. Ignition doesnot controlled rectifier through the trigger transformer operate todischarge the ignition capacitor through the semiconductor controlledrectifier to the high voltage ignition transformer. The enablingtransistor, being turned on with the discharge of the ignition capacitorthrough the semiconductor controlled rectifier, operates to actuate thesaturable oscillator for recharging the ignition capacitor and preparingthe circuit for another cycle. A zener diode connected across the outputof the enabling transistor prevents a ripple in the supply potentialfrom actuating the saturable oscillator, and thus prevents the ignitioncapacitor from being overcharged. v

A diode between the ignition capacitor and the anode of thesemiconductor controlled rectifier improves the response time of thecharging oscillator by isolating other components of the control circuitmeans of the enabling transistor from the high capacitance ignitioncapacitor.

A capacitor in the control circuit means of the enabling transistor andconnected between the anode of the semiconductor controlled rectifierand the reference potential prevents high voltage turnoff spikes fromthe power transformer from shortening the useful life of thesemiconductor controlled rectifier.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a circuit diagram of theinitiation circuit for a capacitor discharge ignition system inaccordance with this invention.

DETAILED DESCRIPTION Referring to the drawing, with the ignition switch12 being closed, the output electrode 66 of the PNP enabling transistor16 of the enabling circuit 21 and the emitter or common electrode 68 ofthe NPN power transistor 14 of the oscillating charging circuit, and thetrigger transformer 18 are energized from a 12 volt wet cell battery 17,which acts as a supply potential, of the kind generally found invehicles or used with outboard motors. The output, or emitter electrode20 of power transistor 14 immediately conducts because of the signalapplied to the base 40 through capacitor 62 and the temperatureresponsive element thermistor 38. The secondary winding 19 of thetrigger transformer 18 produces a voltage on the order of one volt inresponse, for instance, to the opening of the points in the distributorfor activating a semiconductor controlled rectifier 46 to which it isconnected. However, no ignition pulse is applied to the ignitiontransformer because the ignition capacitor 24 is not initially chargedwhen the ignition switch is closed. The ignition capacitor 24 must becharged to about 350 volts before it will operate the ignitiontransfonner 50.

Charging the ignition capacitor 24 is accomplished with the saturableoscillator 41. The oscillator 41 includes the power transistor 14 havingits output, emitter electrode 20 connected to the grounded primarywinding 27 and one termination of the secondary winding 32 of thetertiary transformer 26. Also, secondary winding 32 operates through aparallel combination of the resistor 34 and diode 36 and the temperatureresponsive element 38 connected to the input, base 40 of powertransistor 14 and a rectifier 42 which limits the saturation voltage.The potential at the emitter electrode is fed back to the base 40 orcontrol electrode of power transistor 14 for increasing the outputcurrent to drive the transistor 14 into saturation. The feedback throughsecondary winding 32, parallel combination of resistor 34 and diode 36,and temperature responsive element 38 consequently increases the signalat the base 40 and increases the potential at emitter electrode 20. Oncethe power transistor 14 is driven into saturation, the oscillator shutsoff and capacitor 24, having been charged through secondary winding 28,is ready for discharge through the ignition circuit. The secondarywinding 28 is grounded and connected in series with diode 30 to theignition capacitor 24 and poled to conduct only for the positive halfcycle with respect to reference potential 31 of the signal from theoscillator 41 to charge the ignition capacitor 24. Zener diode 56,connected to the reference'potential 31a the same as collector or commonelectrode 70, clamps the output or emitter voltage of the enablingtransistor 16 at a lower voltage than the supply potential so a ripplingsupply potential generally resulting from a permanent magnet alternatorwill not actuate the saturable oscillator by gating on power transistor14. Consequently overcharging of the ignition capacitor is prevented.Capacitor 24 dielectric is protected from breaking down and its usefullife lengthened along with that of the semiconductor controlledrectifier 46.

Capacitor 44, a component of the control circuit of the transistor 16 ofenabling circuit 21 and connected between the anode of the semiconductorcontrolled rectifier 46 and the reference potential 31, acts as avoltage spike suppressor filtering out the high speed turnoff voltagespikes from the secondary winding 28 when the power transistor 14 turnsoff. With capacitor 44 disconnected and the discharge of the capacitor24, the anode voltage drops to approximately 0, the reference potential,and rapidly rises to approximately 12 volts, as illustrated in waveform39, where it remains while the winding 28 becomes energized. When theoscillator 41 goes into saturation and transistor 14 turns off, a highspeed turnoff voltage spike from the transistor 14 through secondarywinding 28 appears atthe anode of semiconductor controlled rectifier.This spike which is the second spike shown in waveform 39 acts toshorten the life of the semiconductor controlled rectifier 46. After theturnoff of transistor 14 simultaneously with the second spike, thecapacitor 24 begins to charge again to approximately 350 volts which isalso shown in that waveform. Waveform 43, in contrast, displays thevoltage at the anode with capacitor 44 in circuit and the second spike,or turnoff voltage, suppressed. The use of the spike suppressorcapacitor 44 has greatly enhanced the useful life of the semiconductorcontrolled rectifier on the order of 350 hours.

The trigger transformer 18 as heretofore mentioned is periodicallyenergized in timed relation to the engine speed by pulses from thedistributor which may function in either breaker point operation ortiming sensor operation as is well-known in the art. When triggered, thesemiconductor controlled rectifier 46 discharges capacitor 24 throughdiode 45 to the primary winding 48 of the high voltage ignitiontransformer 50.

With each pulse from the trigger transformer 18 the semiconductorcontrolled rectifier 46 is turned on permitting the discharge ofcapacitor 24. Capacitor 44 charges to the same potential as capacitor24. Consequently when the semiconductor controlled rectifier 46 is gatedon the potential at the anode of the semiconductor controlled rectifierwill drop with respect to the voltage across capacitor 44 and diode 64will conduct thus turning on the enabling transistor 16 by applying apulse to control electrode 60. Diode 45 isolates the capacitor 24 fromthe capacitor 44, diode 64 and resistor 65 of the control circuitmeansof the enabling transistor. Consequently, with the semiconductorcontrolled rectifier turned on and conduction occurring, the responsetime of the enabling transistor 16 is rapid. Without diode 45, capacitor24, because of its size and resultant time constant, would have anadverse effect on the speed with which charging would commence.

As the semiconductor controlled rectifier is turned on the control orbase electrode 60 has a change in voltage and the voltage across thetransistor 16 drops sharply. The voltage then returns to its originalvalue with the semiconductor controlled rectifier being turned off,thereby creating a pulse. The pulse driving through capacitor 62 thenactuates the saturable oscillator 41 by turning on transistor 14 tocharge capacitor 24.

With the discharge of capacitor 24, diode 52 provides a feedback pathresulting in a ringout oscillation between the ignition capacitor 24 andthe winding 48. Variable resistance 49 limits the peak voltage operatingsimilarly to a zener diode. The ringout oscillation is very rapidlydamped. When utilized in a conventional outboard motor the ignitiontransformer, as illustrated by oscillating voltage wave 58, will bedamped below the minimum spark gap arcing voltage level in approximatelymicroseconds, as illustrated by oscillating voltage wave 58. Analternating current spark is effected at spark gap 54 as activated bythe high voltage ignition transformer 50. The alternating current sparkat spark gap 54 prevents the hot oil and gas mixture in the cylinderfrom depositing in the spark gap. The invention thus prevents spark gapfouling and reduces the frequency of spark plug replacement.

What we have, therefore, is an initiation circuit for a capacitordischarge ignition system which includes an enabling circuit forpreventing overcharging of the ignition capacitor, protecting thesemiconductor controlled rectifier from high voltage spikes of shortduration, prolonging the semiconductor controlled rectifiers usefullife, and improving the response time of the oscillating circuit forcharging the ignition capacitor.

1 claim:

1. An initiation circuit for a capacitor discharge ignition system foran internal combustion engine comprising an ignition capacitor; asemiconductor trigger means for discharging said ignition capacitor insynchronism with the engine to produce ignition pulses, saidsemiconductor trigger means having a gate, an input and an output; anoscillating circuit comprising a power transistor having control andoutput electrodes,

a transformer having a primary winding connected between said output ofsaid power transistor and a reference potential and having first andsecond inductively coupled secondary windings, and circuit means forcoupling said first secondary winding between said output and controlelectrode of said power transistor, said primary inducing current insaid first secondary winding to drive said-power transistor intosaturation; an enabling circuit having an enabling transistor withcontrol, output and common electrodes with said common electrode beingconnected to a reference potential, a zener diode connected between saidoutput and common electrodes and poled to prevent changes in themagnitude of the supply potential from initiating the power transistorof said oscillating circuit, control circuit means coupling said inputof said semiconductor controlled rectifier to said control electrode ofsaid enabling transistor, said output electrode of said enablingtransistor being responsive to the operation of the semiconductortrigger means to couple a signal from the input of the trigger means tothe control electrode of the power transistor; capacitor means coupledbetween said output electrode of said enabling transistor and saidcontrol electrode of said power transistor to isolate said enablingtransistor from said oscillating circuit; a supply potential coupled tosaid common electrode of said power transistor; circuit means couplingsaid supply potential to the output of said enabling transistor, a firstelectron control device and said secondary winding of said transformerin series and coupled across said ignition capacitor with induced pulsesof one polarity from said second secondary winding charging saidignition capacitor; and an ignition transformer having primary andsecondary windings and connected to said output of said semiconductortrigger means.

2. An initiation circuit for a capacitor discharge ignition systemaccording to claim 1 wherein said control circuit means includes a diodeproviding isolation from said ignition capacitor to improve the responsetime of said enabling transistor.

3. An initiation circuit for a capacitor discharge ignition systemaccording to claim 1 wherein said control circuit means includes acapacitor connected between the input of said trigger means and saidreference potential for filtering out voltage spikes resulting from saidsaturable oscillator turning off.

4. An initiation circuit for a capacitor discharge ignition systemaccording to claim 1 including an electron control device connectedbetween said primary of said ignition transformer and said ignitioncapacitor to provide a feedback path for producing a ringout oscillationbetween the ignition capacitor and said ignition transformer, saidringout oscillation producing an alternating current across said sparkgap.

5. An initiation circuit for a capacitor discharge ignition system foran internal combustion engine comprising an ignition capacitor; asemiconductor controlled rectifier for discharging said ignitioncapacitor in synchronism with the engine to produce ignition pulses,said semiconductor controlled rectifier having a gate, an anode, and acathode; a power transistor for charging said ignition capacitor, saidpower transistor having control, output and common electrodes, a supplypotential coupled to said reference electrode of said power transistor;a transformer having first, second and third inductively coupledwindings with the output electrode of said power transistor beingcoupled to said first winding; circuit means for connecting said secondwinding to said control electrode of said power transistor withincreases in current in said first winding increasing current in saidsecond winding and driving said power transistor into saturation withsaid ignition capacitor being charged; a first diode and said thirdwinding in series and coupled across said ignition capacitor withinduced pulses of one polarity in said third winding charging saidignition capacitor; an enabling circuit having an enabling transistorwith control, output and common electrodes, control circuit meanscoupling said control electrode of said enabling transistor to saidanode of said semiconductor controlled rectifier for activating saidenabling transistor, said output electrode of said enabling transistorbeing coupled .to said supply potential, and said common electrode beingcoupled to said reference potential; a zener diode being connectedbetween said common and output electrodes of said enabling transistorand being poled to prevent changes in magnitude of said supply potentialfrom initiating said power transistor; an ignition transformer having aprimary winding and a secondary winding and being connected to thecathode of said semiconductor controlled rectifier; a capacitor coupledbetween said output of said enabling transistor and said controlelectrode of said power transistor for initiating said power transistorwith said enabling transistor being activated; first diode means coupledbetween said ignition capacitor and said anode of said semiconductorcontrolled rectifier means to improve the response time of said enablingtransistor, second diode means coupled between said output of saidtrigger means and said ignition capacitor and poled to create a ringoutoscillation between said ignition capacitor and said primary of saidignition transformer for producing an alternating current ignitionpulse, a capacitor connected between said anode of said semiconductorcontrolled rectifier means and said reference potential to filterturnoff spikes from said third winding with said power transistorturning off to prevent damage to said semiconductor controlled rectifiermeans.

1. An initiation circuit for a capacitor discharge ignition system foran internal combustion engine comprising an ignition capacitor; asemiconductor trigger means for discharging said ignition capacitor insynchronism with the engine to produce ignition pulses, saidsemiconductor trigger means having a gate, an input and an output; anoscillating circuit comprising a power transistor having control andoutput electrodes, a transformer having a primary winding connectedbetween said output of said power transistor and a reference potentialand having first and second inductively coupled secondary windings, andcircuit means for coupling said first secondary winding between saidoutput and control electrode of said power transistor, said primaryinducing current in said first secondary winding to drive said powertransistor into saturation; an enabling circuit having an enablingtransistor with control, output and common electrodes with said commonelectrode being connected to a reference potential, a zener diodeconnected between said output and common electrodes and poled to preventchanges in the magnitude of the supply potential from initiating thepower transistor of said oscillating circuit, control circuit meanscoupling said input of said semiconductor controlled rectifier to saidcontrol electrode of said enabling transistor, said output electrode ofsaid enabling transistor being responsive to the operation of thesemiconductor trigger means to couple a signal from the input of thetrigger means to the control electrode of the power transistor;capacitor means coupled between said output electrode of said enablingtransistor and said control electrode of said power transistor toisolate said enabling transistor from said oscillating circuit; a supplypotential coupled to said common electrode of said power transistor;circuit means coupling said supply potential to the output of saidenabling transistor, a first electron control device and said secondarywinding of said transformer in series and coupled across said ignitioncapacitor with induced pulses of one polarity from said second secondarywinding charging said ignition capacitor; and an ignition transformerhaving primary and secondary windings and connEcted to said output ofsaid semiconductor trigger means.
 2. An initiation circuit for acapacitor discharge ignition system according to claim 1 wherein saidcontrol circuit means includes a diode providing isolation from saidignition capacitor to improve the response time of said enablingtransistor.
 3. An initiation circuit for a capacitor discharge ignitionsystem according to claim 1 wherein said control circuit means includesa capacitor connected between the input of said trigger means and saidreference potential for filtering out voltage spikes resulting from saidsaturable oscillator turning off.
 4. An initiation circuit for acapacitor discharge ignition system according to claim 1 including anelectron control device connected between said primary of said ignitiontransformer and said ignition capacitor to provide a feedback path forproducing a ringout oscillation between the ignition capacitor and saidignition transformer, said ringout oscillation producing an alternatingcurrent across said spark gap.
 5. An initiation circuit for a capacitordischarge ignition system for an internal combustion engine comprisingan ignition capacitor; a semiconductor controlled rectifier fordischarging said ignition capacitor in synchronism with the engine toproduce ignition pulses, said semiconductor controlled rectifier havinga gate, an anode, and a cathode; a power transistor for charging saidignition capacitor, said power transistor having control, output andcommon electrodes, a supply potential coupled to said referenceelectrode of said power transistor; a transformer having first, secondand third inductively coupled windings with the output electrode of saidpower transistor being coupled to said first winding; circuit means forconnecting said second winding to said control electrode of said powertransistor with increases in current in said first winding increasingcurrent in said second winding and driving said power transistor intosaturation with said ignition capacitor being charged; a first diode andsaid third winding in series and coupled across said ignition capacitorwith induced pulses of one polarity in said third winding charging saidignition capacitor; an enabling circuit having an enabling transistorwith control, output and common electrodes, control circuit meanscoupling said control electrode of said enabling transistor to saidanode of said semiconductor controlled rectifier for activating saidenabling transistor, said output electrode of said enabling transistorbeing coupled to said supply potential, and said common electrode beingcoupled to said reference potential; a zener diode being connectedbetween said common and output electrodes of said enabling transistorand being poled to prevent changes in magnitude of said supply potentialfrom initiating said power transistor; an ignition transformer having aprimary winding and a secondary winding and being connected to thecathode of said semiconductor controlled rectifier; a capacitor coupledbetween said output of said enabling transistor and said controlelectrode of said power transistor for initiating said power transistorwith said enabling transistor being activated; first diode means coupledbetween said ignition capacitor and said anode of said semiconductorcontrolled rectifier means to improve the response time of said enablingtransistor, second diode means coupled between said output of saidtrigger means and said ignition capacitor and poled to create a ringoutoscillation between said ignition capacitor and said primary of saidignition transformer for producing an alternating current ignitionpulse, a capacitor connected between said anode of said semiconductorcontrolled rectifier means and said reference potential to filterturnoff spikes from said third winding with said power transistorturning off to prevent damage to said semiconductor controlled rectifiermeans.